Non-oriented wire in elastomer electrical contact

ABSTRACT

A method and apparatus for interconnecting an electronic module to a substrate through resilient wire conductors in an interposer arrangement. A carrier layer of insulating material with an array of apertures, arranged to align with both the electrical pads on an electronic module and electrical contacts on a substrate, each hold, for example, a resilient wadded wire connector. Each connector extends through the aperture provided and beyond the upper and lower surfaces of the carrier layer. Each resilient wadded wire connector and aperture is encapsulated with a elastomeric insulating material sufficiently deformable so as to allow said resilient wadded wire connector to deform upon application of a normal force from each side tending to depress the connector into its aperture. The encapsulation prevents loss or smear of a wadded wire connector when handling.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to electronic packaging. Moreparticularly, the present invention relates to electronic interposersused in electronic packaging to make electrical connection of electronicmodules to printed wiring boards, and the like.

2. Background and Related Art

Compression connectors, such as those employed in land grid array (LGA)connections, are well known in the art. Typical LGA compressionconnections employ an interposer to connect a single chip or multiplechip module (MCM) to a printed wiring board (PWB). The MCM generallycomprises multiple integrated circuits or chips assembled into asubsystem the size of traditional single chip packages. The single chipor MCM may be connected to the PWB through the interposer with the chipmodule circuit pads making contact with the array of connection pointsextending from one surface of the interposer and the PWB circuit padsmaking contact with the array of connections extending from the othersurface of the interposer. Compression forces are employed to hold thechip module and PWB against the interposer.

Various forms of interposers have been designed to facilitate the LGAconnection of the single chip or MCM to the PWB. One of theconsiderations in designing interposers is to create a structure thatwill accommodate the thermal mismatch between chip module and PWB.Another consideration in designing interposers is to create a structurethat will accommodate differences in topography between the matingsurface profiles and mating conductor of the chip module and PWB.

Interposer layers of both substantially rigid and relatively resilientinsulating materials have been employed for this purpose. In using suchmaterials, a variety of conductor interconnect structures have beenemployed in the prior art to electrically connect the contacts or padson one surface of the interposer to the corresponding contacts or padson the other surface of the interposer. One form of conductorinterconnect structure employed is designed to be resilient ordeformable. As such, the deformable conductor can move to accommodate,for example, the CTE dimensional mismatch between the chip module andPWB.

One example of a resilient or deformable conductor used in rigid orsemi-rigid layers of insulating material is the resilient wadded-wireconnector, sometimes also known as the “fuzz-button” type connector orthe connector made by CINCH Connectors, Inc. under the trademarkCIN::APSE. An example of such type of connector is found in U.S. Pat.No. 6,386,890. The interposer in such arrangements typically comprises asubstantially rigid interposer layer of plastic having a plurality orarray of apertures with each aperture further having disposed thereon adeformable, randomly configured, resilient conductor material forconnecting a MCM, for example, to a PWB. The resilient conductors ofwadded wire are typically held by friction within a plastic layer.

Such wadded-wire button or connector arrangements have proven to bereliable once assembled but have been found somewhat difficult to handlebeforehand without causing damage to, or displacement of, thewadded-wire button connector. Contact with the wadded-wire buttonconnectors in handling may result in missing button connectors orpulled/smeared button connectors. Since the connectors are typicallyretained in the interposer layer by friction, they are prone to beingpushed or pulled from position. In addition, handling may result insmearing a button connector wherein handling contact with the connectorcauses a portion of the wadded-wire to become unwadded and free of theaperture wherein it may extend across the surface of the interposermaterial and short to the wadded-wire button connector of an adjacentaperture.

FIG. 1 depicts an example of a typical wadded-wire button connectorarrangement which, as can be seen, is randomly wound. An array of ninesuch connectors is shown to illustrate the connector arrangement but itis understood that, in practice, the array of connectors would typicallybe made much greater. As shown in FIG. 1A, wadded-wire connectors 1 areheld by friction in apertures 3 in insulating layer 5. As shown in FIG.1B, the wire of button connector 1 has been smeared to unwind portion 7such that it could short to an adjacent wadded wire button connector.

SUMMARY OF THE PRESENT INVENTION

It is, therefore, an object of the present invention to provide animproved electronic package.

It is a further object of the present invention to provide an improvedmethod and apparatus for connecting an electronic module to a substratetherefor.

It is yet a further object of the present invention to provide animproved interposer structure for connecting an electronic module to asubstrate, such as, a PWB.

It is yet still a further object of the present invention to provide aresilient wadded-wire button connector interposer structure with theconnectors encapsulated within a compliant or deformable elastomericinsulator material to thereby increase reliability of the interposerstructure.

It is another object of the present invention to provide arigid/semi-rigid or resilient interposer insulating layer with an arrayof apertures containing wadded-wire connectors encapsulated with acompliant elastomeric insulating material sufficient to retain andcontain the wound wadded-wire but yet which elastomeric may besufficiently soft to deform and allow the wadded-wire to protrudetherethrough under compression between electronic module and substrate.

In accordance with the present invention, there is provided an improvedLGA connector for connecting an electronic module, such as a single chipor MCM module, to a substrate, such as a PWB. The LGA connectorcomprises at least one carrier layer of dielectric insulating materialhaving an array of apertures each holding randomly wound wadded-wireconnectors. The connectors are encapsulated with a complianteleastomeric material, preferably having a relatively low modulus, toretain and contain the wadded wire so as to protect the wires from beingpulled or lost. The elastomeric material may be sufficiently soft sothat the wadded-wire member protrudes through the elastomeric materialduring activation of the compressive force used to make acompression-type connection of the electronic module to the substrate.Alternatively, a laser or the like may be employed to oblate theelastomeric material in the contact region to expose the wadded wire.

The carrier layer of insulating material may comprise material that is arigid/semi-rigid insulator or a flexible insulator. Multiple layers ofcombinations of such material may also be employed. Instead of randomlywound wadded-wire, a tubular wire structure may be used for theconducting member. In such an arrangement, the tube would preferably beoriented on its side with the plane of the wire loops leaning somewhatto provide a linear force versus deflection characteristic.

BRIEF DESCRIPTION OF THE DRAWING

FIGS. 1A and 1B show the prior art structure of an interposer withwadded-wire button connectors.

FIGS. 2A and 2B show cross-sectional views of two arrangements ofencapsulated wadded-wire connectors in a rigid/semi-rigid insulatingcarrier layer, in accordance with the present invention.

FIGS. 3A–3C show cross-sectional views of further arrangements ofencapsulated wadded-wire connectors in a flexible insulating carrierlayer, in accordance with the present invention.

FIGS. 4A and 4B respectively show a cross-sectional side and end view ofa still further arrangement of encapsulated wadded-wire connectors, andmethod of forming same, is a rigid/semi-rigid insulating carrier layer,in accordance with the present invention.

FIGS. 5A and 5B show perspective views of one arrangement of upper andlower mold halves used to fabricate one arrangement of encapsulatedwadded-wire connectors, in accordance with the present invention.

FIG. 5C shows a cross-sectional view of the mold halves of FIGS. 5A and5B positioned on an insulating carrier layer.

FIGS. 6A and 6B shows perspective views of another arrangement of moldhalves used to fabricate another arrangement of encapsulated wadded-wireconnectors, in accordance with the present invention.

FIG. 6C shows a cross-sectional view of the mold halves of FIGS. 6A and6B positioned on an insulating carrier layer.

FIG. 7 shows a cross-sectional view of an interposer arrangement, inaccordance with the present invention, positioned between an electronicmodule and substrate therefor.

DETAILED DESCRIPTION

With reference to the prior art arrangement shown in FIGS. 1A and 1B, ashereinabove described, handling of the insulating carrier layer withwadded-wire connectors exposed, as shown, may result in loss of thecomplete connector or the smearing of connectors, as shown by wire leadportion 7 in FIG. 1B. Handling may occur, for example, in the assemblyprocess of connecting the electronic module to a PWB, for example.

FIG. 2A shows one arrangement for encapsulating randomly woundwadded-wire connectors. In this arrangement, a conventional plasticrigid/semi-rigid insulating carrier layer 25A, is configured, forexample, as generally shown in FIGS. 1A–1B, with an array of aperturesholding wadded-wire connectors. As further shown in FIG. 2A, theconnectors are overmolded with an elastomeric polymer material 29A so asto encapsulate wadded-wire connectors 21A. This may be done in a mannerso as to leave the contact tips of wire loops and leads of connectors21A exposed. Alternatively, encapsulating material covering the contacttips of wire loops and leads may be laser ablated, for example to exposethe contact tips.

The elastomeric polymer encapsulating material may be any of a varietyof elastomeric polymer materials. For example, the encapsulating polymermaterial may be an elastomeric silicone, such as, SYLGARD No. 182 madeby Dow Corning or an elastomeric epoxy, such as, Epo-Tek No. 310 made byEpoxy Technology. The elastomeric encapsulating material may also besufficiently thin, soft and deformable so as to allow the contact tipsof the wadded-wire connectors to punch through the material and therebyexpose the contact tips. As can be seen, the contact tips are thus theloops and leads of the wadded-wire at the interface surfaces to theelectronic module and substrate, respectively. The modulus of eachelastomeric material would typically be less than 5000 psi and,preferably, less than 2000 psi.

The rigid/semi-rigid insulating carrier layers 25A and 25B in FIGS. 2Aand 2B may be made of, for example, liquid crystal polymer materials,such as, VECTRA's No. A 130 liquid crystal polymer material.Alternatively, nylon or polyphenylene sulfides, such as, RYTON (Phillips66), or polycarbonates, such as LEXAN, (GE) may be used. The range ofmodulus for such materials is 377,000 psi to 2,175,000 psi. Thewadded-wire connectors are typically randomly wound wadded resilientwire made of molybdenum, beryllium-copper or other electricallyconductive metallic member.

The encapsulated wadded-wire conductor arrangement of FIG. 2A may befabricated using the mold arrangement shown in FIGS. 5A–5C. The top halfof the mold block 52A is shown in FIG. 5A. Apertures 53A in block 52Aprovide space to encapsulate the top portion of the wadded-wire thatextend from the surface of the insulating carrier layer. Although onlynine apertures are shown for illustrative purposes, it is clear that inpractice, there would be a large number of apertures arrayed in block52A. The recessed region 58A provides the mold throat/mold layer areawhere liquid mold material is poured in to form elastomeric polymerencapsulated wadded-wire connectors that extend from a layer ofelastomeric polymer material. It is clear that the thickness of thelayer of elastomeric polymer material is determined by the depth ofrecessed region 58A. This layer is shown as layer 27A in FIG. 2A, andthe thickness of the layer is selected in accordance with design choice.Apertures 54A provide alignment holes for alignment pins.

FIG. 5B shows a similar mold block configuration for the bottom half ofmold 52B. However, in the arrangement of FIG. 5B, mold block 52Bcomprises a split mold block. Mold block 52B is split along line 56Bwith bottom portion 59B being removable. As shown, block line 56B risesin the mid-section in the area of the apertures 53B to reduce and definethe depth of the aperture array in the upper portion 50B of block 52B.In this regard, the aperture or cavity walls of apertures 53B may bevertical or tapered. FIGS. 3A–C show tapered walls. It is clear thatwhichever wall configuration is used, the aperture wall configurationwould be the same in both the top half mold block 52A, in FIG. 5A andbottom half mold block 52B, in FIG. 5B.

It should be understood that bottom portion 59B of mold block 52B isremovable to facilitate removal of the cast part. Thus, with removal ofbottom portion 59B of mold block 52B, the cast part may be pushed outwithout damage. After removal of the cast part from mold block 52B, theupper half mold block 52A may be readily removed from the cast part. Itis clear, however, that both mold block 52A in FIG. 5A and mold block52B in FIG. 5B may be split mold blocks, similar to that shown in FIG.5B.

It is also clear that removable portion, such as bottom portion 59B ofmold block 52B, may be used to facilitate assembly of parts beforecasting. Thus, after separating the removable bottom portion 59B fromblock 52B, wadded wire buttons may be inserted into the cavities 53Bfrom below, through apertures in the insulating carrier layer and intothe cavities 53A of the upper block half 52A. This can be seen moreclearly with reference to FIG. 5C.

In FIG. 5C, the top half of the mold shown in FIG. 5A is positioned onthe bottom half of the mold shown in FIG. 5B. Pins in alignment holes54A and 54B act to position and align the mold halves. Any of a varietyof arrangements may be employed to clamp the mold halves together. Arigid/semi-rigid insulating carrier layer 55 is positioned between themold halves. Insulating carrier layer 55 may be, for example, arigid/semi-rigid insulating carrier layer, like carrier layers 25A and25B shown in FIGS. 2A and 2B, respectively. With bottom portion 59B ofmold block 52B removed, wound wadded-wire connectors 51 may be pushed upinto apertures 53B, 53 and 53A prior to encapsulation.

Alternatively, prior to positioning the top mold half and bottom moldhalf together, wadded-wire conductors 51 may be positioned in apertures53 of insulating carrier layer 55 where they are held in place byfriction. The mold halves may then be positioned over the wadded-wireconnectors 51 so that the connectors are positioned in apertures 53A and53B. Liquid elastomeric polymer material is then poured into moldthroat/mold layer regions 58A/58B and cured.

It should be understood that the mold arrangements described herein aremerely examples of ways in which the wadded-wire connectors may beencapsulated. It is clear that there are any of a variety of ways inwhich an rigid/semi-rigid and flexible insulating carrier layer withencapsulated wadded wire connectors may be fabricated.

In the arrangement of FIG. 2A, apertures 23A in insulating carrier layer25A are approximately the same size or slightly smaller than theelastomeric encapsulation 29A over wadded-wire connectors 21A. Thus, themold apertures and insulating carrier layer apertures used in FIG. 2Aare approximately the same dimension, as shown in FIG. 5C. In FIG. 2B,however, the apertures 23B in insulating carrier layer 25B areconsiderably smaller than the apertures in the mold blocks 53A and 53Bin FIG. 5. The main consideration in either arrangement is that theconnector be completely encapsulated. In this regard, it should beunderstood that the drawings are not to scale nor is the size shown forcorresponding parts, as depicted among the various figures, accuratelyrelated to one another.

FIG. 3A shows another interposer arrangement with wadded wire connectorsencapsulated with elastomeric polymer material. In FIGS. 3A–C, theinsulating carrier layers 35A, 35B and 35C may be made of a flexibledielectric material, such as, KAPTON. Materials, such as, UPILEX andepoxy coated woven glass, such as, G10, may also be used, as well asFR4. The modulus for such material may range from 435,000 psi to1,305,000 psi. The mold arrangement of FIG. 5 may be used to form theinterposer of FIG. 3 with the thickness of elastomeric polymer layer 37Aformed on carrier layer 35A being selected to provide the desired degreeof stiffness for handling, assembly and thermal cycling. Typically, thethickness of polymer layer 37A would be 5 to 10 mils. As shown, theelastomeric encapsulation 39A has sloped walls thus necessitating sameslope in the aperture of the mold blocks.

Again, the elastomeric polymer material used for encapsulation may besufficiently soft and thin along the flat interfacing surface of theelastomeric encapsulations such that when the interposer of FIG. 3A isclamped between electronic module and PWB, for example, loops and leadsof the distal portion of wadded-wire connectors may push through thematerial skin to make contact with the electrical contacts of theelectronic module and PWB. Alternatively, the elastomeric encapsulationsmay be ablated to expose the wire conductors.

The interposer arrangement of FIG. 3A may be made even thinner byeliminating the formation of the layer of elastomeric material 37A, asshown in FIG. 3A, on the flexible insulating carrier layer 35A. Thethinner arrangement is shown in FIG. 3B. This may be accomplished in anyof a variety of ways, such as with the mold arrangement shown in FIGS.6A–C. As can be seen, the mold blocks 62A and 62B are the same as thatshown in FIGS. 5A–C with the exception that no recessed regions, asshown at 58A and 58B is FIG. 5, are provided in FIGS. 6A–C. Withoutthese recessions, encapsulation on flexible carrier layer 65 shown inFIG. 6C is limited to the aperture regions 63A and 63B, as shown in FIG.6C. Again, although the apertures 63A and 63B are shown with verticalcylindrical walls, it is clear that the walls would slope for theencapsulation arrangements of FIGS. 3B–C.

The carrier layer 35B of the interposer arrangement of FIG. 3B may bemade rigid/semi-rigid by adding additional stiffening layers 37C onopposing surfaces thereof between encapsulations 39C, as shown in FIG.3C. These stiffening layers may be formed first and then bonded toflexible carrier layer 35C or alternatively, may be deposited thereonusing some form of deposition technique, such as, vapor deposition,sputtering, or the like.

It should be understood that in any of the interposer arrangements shownin FIGS. 2A–C, FIGS. 3A–C and FIGS. 4A–B, that fewer or more layers maybe employed in the insulating carrier layer without departing from thespirit of the invention. Included in these layers may be electricallyconductive layers to provide shielding or reference planes as well aspoint to point wiring as known in the printed circuit wiring board artto electrically connect selected wadded wires contacts. In addition,multiple layers of the same or different materials may be employedconsistent with the encapsulation of the wadded-wire conductors, asdescribed herein.

FIGS. 4A–B show a further interposer arrangement wherein the insulatingcarrier layer includes a molding channel/runner for encapsulating thewadded-wire connectors. Thus, insulating carrier layer 45 in FIGS. 4A–Bmay comprise a rigid/semi-rigid insulating material, similar to thatshown in FIGS. 2A–B. Molding channel/runner 46 is shown as a through cutin the top portion of insulating carrier layer 45, as shown in FIG. 4B.Molding channel 46 acts to provide a path in which to feed liquidelastomeric insulating encapsulating material to form wireencapsulations 49. It is clear that channel 46 also includes a runner ofhardened encapsulant when the molding process is completed and theencapsulant is cured.

It can be seen that the molding channel/runner 46 shown in FIGS. 4A–Bacts to feed one row of apertures 43 in insulating carrier layer 45. Inpractice, however, to encapsulate an array of wadded wire conductorsheld in the apertures of an insulating carrier layer, it is clear thatthere would be a molding channel for each row or column of apertures.Alternatively, both rows and columns of molding channels intersecting atapertures in the carrier layer could be employed. The mold blocks shownin FIGS. 6A–C may be employed to fabricate the encapsulation arrangementshown in FIGS. 4A–B.

FIG. 7 shows a cross-sectional view of the flexible interposerarrangement similar to that of FIG. 3A, as positioned between electronicmodule 73, such as a MCM, and substrate 77, such as a PWB. Conductivepads 76 on module 73 and conductive contacts 78 on substrate 77 areconventional metal pads and contacts made of, for example, copper or thelike. Compressive force applied to module 73 and backing layer 80 onsubstrate 77 acts to clamp the arrangement together. A typical clampingforce is one that would provide an upward normal force of at least about30 grams against conductive pads 76 and a downward normal force of atleast 30 grams against conductive contacts 78. The clamping force mayalso act to force the loops and leads of wadded-wire connectors 71through the flat skin surface of elastomeric encapsulation region 79 ateach interface with pads 76 and contacts 78 to make electrical contacttherewith. In addition, the wadded-wire connectors 71 may deformthemselves within the encapsulation as elastomeric encapsulation regions79 deform under compressive force.

The overall resilience of the flexible carrier layer 75, deformableelastomeric encapsulation regions 79 and resilient wadded-wireconnectors, as shown in FIG. 7, acts to ensure good electrical contactbetween module and substrate with the overall resilience acting toaccommodate thermal and dimensional mismatch between module andsubstrate. It is clear that in similar manner, that any of the variousinterposer arrangements described herein will act as the arrangement ofFIG. 3A to provide a resilient connection between electronic module andsubstrate therefor. Thus, in similar manner, the rigid/semi-rigidinsulator carrier layers with elastomeric encapsulation of wadded-wireconnectors provides resilience through the elastomeric encapsulationmaterial and wadded wire connector. It is also clear that other forms ofresilient connectors may be used. For example, a tubular wire structuremay be used with the tube oriented on its side, as described above.

The advantages of employing an elastomeric encapsulated wadded-wireconnector, in addition to its ability to deform, reside in the fact thatthere is resilient metal-to-metal contact at the opposing interfaces ofthe interposer. In addition, the contact is multi-pointed, through loopsand leads, with one continuous conductor. By encapsulating thewadded-wire connectors, the connectors are captivated such as to preventthem from falling out and the loops and leads of the connector be notexposed to possible pulls and snags to smear the connector.

It will be understood from the foregoing description that variousmodifications and changes may be made in the preferred embodiment of thepresent invention without departing from its true spirit. It is intendedthat this description is for purposes of illustration only and shouldnot be construed in a limiting sense. The scope of this invention shouldbe limited only by the language of the following claims.

1. An electronic module to substrate interconnecting structure,comprising: at least one layer of insulating material having opposingsurfaces and an array of apertures formed therethrough to each of saidopposing surfaces; a plurality of wound wadded wire connectors formed toprovide deformable resilient electrical conductors with individual onesof said conductors disposed within respective ones of said apertures ofsaid array of apertures of said at least one layer of insulatingmaterial so that distal portions of said resilient electrical conductorsextend beyond said opposing surfaces of said layer of insulatingmaterial with said distal portions including loops and leads; andelastomeric insulating material disposed around each of said deformableresilient electrical conductors and corresponding ones of said aperturesholding said conductors to encapsulate said electrical conductors, saidelastomeric insulating material forming a thin solft layer over saidloops and leads with said layer being sufficiently thin and soft so asto allow said loops and leads to extend therethrough under compressionthereof.
 2. The interconnecting structure as set forth in claim 1wherein the modulus of said elastomeric insulating material is less than2000 psi.
 3. The interconnecting structure as set forth in claim 1wherein said elastomeric insulating material is selected from the groupincluding epoxy and silicone elastomers.
 4. A substrate to electronicmodule mounting and interconnecting structure, comprising: a substratehaving a top surface; a plurality of electrical contacts on saidsubstrate top surface; an electronic module having a plurality ofelectrical pads for respective electrical connection to said pluralityof electrical contacts on said substrate top surface; an interposerlayer of insulating material having an upper and lower surface and anarray of apertures extending from said upper surface to said lowersurface with respective ones of said array of apertures positioned to bealigned with respective ones of said plurality of electrical contacts onsaid substrate top surface and said plurality of electrical pads on saidelectronic module, each of said respective ones of said array ofapertures having disposed therein a deformable resilient electricalconductor of randomly wound wire to form a wadded wire connectorextending through said apertures and beyond said upper surface and saidlower surface, each said wadded wire connector encapsulated with anelastomeric polymer insulating material to retain said wire connectorand with said elastomeric insulating material around the distal portionof each said wadded wire connector extending beyond said upper surfaceand said lower surface being sufficiently thin and soft so as to allowsaid wadded wire connector to extend therethrough under compressionforce to make electrical contact between said electrical pads on saidelectronic module and said electrical contacts on said substrate; andmeans to apply compression force to clamp said electronic module to saidsubstrate wherein each said encapsulated wadded wire conductor makeselectrical connection between said electronic module and substrate. 5.The interconnecting structure as set forth in claim 4 wherein themodulus said elastomeric insulating material is less than 5000 psi.